2003 Tahoe coolant system leak or head gasket leak?

[tomloans]

Just let quality synthetic oil do its thing!

Did you check under that passenger side cover?

I haven't yet but looking for a response from Blackstone. If coolant is in the water then they both come off whether or not these old eyes can see anything or not. I am realtively certain it is all coming off shortly. LOL. Question for you. Do the 799 heads require premium gas or can I continue to use 87 Octane?

 

[tomloans]

NICE!

Not bragging, here, either.

195K miles:

View attachment 362962

View attachment 362963

Woe the first time I looked I only saw the covers, but I just saw the top of the cylinder head. I am not worthy! I am not worthy!

 

[rayra]

Had a similar mystery leak, found the info about the Castech heads problem, confirmed the cracks in the head under the rockers, got a package of ACDelco stop-leak tablets mentioned in the related service bulletin and it stopped the problem. I've since put a couple years and some very hard towing miles, high revs high heat, on that motor with no recurrence of the issue.

 

[iamdub]

I haven't yet but looking for a response from Blackstone. If coolant is in the water then they both come off whether or not these old eyes can see anything or not. I am realtively certain it is all coming off shortly. LOL. Question for you. Do the 799 heads require premium gas or can I continue to use 87 Octane?

799 (same as 243) would actually lower the compression a hair, so you'd definitely be safe with 87 octane. The heads do flow better than the 706s, but that only helps top-end power. You may or may not notice any loss from the reduced compression. If you had the heads milled, you'd maintain your stock compression (or improve it a tiny smidge) AND benefit from the higher flow, so it'd be a win-win. But, not really much of a loss if you didn't. For the minimal cost, my preference is to have them professionally cleaned and milled.

 

[iamdub]

Woe the first time I looked I only saw the covers, but I just saw the top of the cylinder head. I am not worthy! I am not worthy!

lol

I don't know what oil the original owner used, but they definitely had it changed regularly. I bought the Tahoe at 146K and ran either Mobil1 or Pennzoil Platinum, changed every 5K. The teardown in my build thread shows the results of quality synthetic oil changed regularly.

That dirty cover is one I bought to get the updated design. I pulled mine off (the clean one) and saw that I already had the updated one.

 

[Fless]

That dirty cover is one I bought to get the updated design. I pulled mine off (the clean one) and saw that I already had the updated one.

Good thing you cleared that up, since I was having trouble seeing any difference, except for clean vs. dirty.

 

[iamdub]

Good thing you cleared that up, since I was having trouble seeing any difference, except for clean vs. dirty.

Yeah, I see that was kinda redundant.

Back up off me- I'm weaning myself off coffee.

 

[tomloans]

799 (same as 243) would actually lower the compression a hair, so you'd definitely be safe with 87 octane. The heads do flow better than the 706s, but that only helps top-end power. You may or may not notice any loss from the reduced compression. If you had the heads milled, you'd maintain your stock compression (or improve it a tiny smidge) AND benefit from the higher flow, so it'd be a win-win. But, not really much of a loss if you didn't. For the minimal cost, my preference is to have them professionally cleaned and milled.

Good to know. Waiting on Blackstone at thr moment to confirm coolant in oil. With a job this big, I want to be absolutely sure. I likely will need your help again. Be in touch soon.

 

[tomloans]

Had a similar mystery leak, found the info about the Castech heads problem, confirmed the cracks in the head under the rockers, got a package of ACDelco stop-leak tablets mentioned in the related service bulletin and it stopped the problem. I've since put a couple years and some very hard towing miles, high revs high heat, on that motor with no recurrence of the issue.

 

[tomloans]

The tablets are definitely tempting for sure. I just can't believe they would stop a crack in the cylinder head. Just to be sure, are you certain you had that crack? Did you stop losing radiator fluid or is it just a slower loss?